Partially hydrogenated block copolymers of vinyl aromatic and conjugated dienes such as hydrogenated styrene-butadiene-styrene copolymers are well known in the art. U.S. Pat. Nos. 3,333,024; 3,431,323; 3,598,886; 5,352,744; 3,644,588 and EP-505,110 disclose various hydrogenated block copolymers. Partially hydrogenated refers to hydrogenation of the diene portion of the block copolymer without aromatic hydrogenation or aromatic hydrogenation of 90 percent or less. Although these partially hydrogenated copolymers have been tested in various applications, they suffer from one or more shortcomings, including low heat resistance, poor physical properties, poor processability, and poor light stability. Attempts have been made to remedy these shortcomings by increasing the hydrogenation of the aromatic ring of the block copolymer. However, polymer scientists contend that fully hydrogenated styrene-butadiene-styrene copolymers have no useful properties at elevated temperatures, even if only slightly elevated. Thermoplastic Elastomers, 2nd edition, 1996, page 304, lines 8-12 states “Thus, polystyrene remains the choice for any amorphous hydrocarbon block copolymer. This last fact is clearly demonstrated in the case of the fully hydrogenated VCH-EB-VCH polymer. The interaction parameter is so severely reduced by hydrogenation that at only slightly elevated temperatures, the polymer loses all strength and appears to be homogeneously mixed at ordinary melt temperatures.”
Specifically, hydrogenated diblock copolymers tend to have low viscosities and melt strengths making them difficult to process. Diblocks also have other disadvantages, due to their poor tensile properties. For the same reason they are not useful for making flexible materials, while rigid materials made from hydrogenated diblocks tend to be brittle.
Blends of partially hydrogenated block copolymers with other polymers are also known. For example, blends of cyclic olefin (co)polymers have been attempted as disclosed in EP-0726291, wherein cyclic olefin (co)polymers are blended with vinyl aromatic/conjugated diene block copolymers or hydrogenated versions thereof. Cyclic olefin (co)polymers (COC's) are known to have excellent heat distortion temperature, UV stability and processability. However, such copolymers suffer from poor impact resistance. Blends of COC's with partially hydrogenated block copolymers still suffer from an imbalance of physical properties due to the absence of aromatic hydrogenation within the block copolymer.
Therefore, there remains a need for compositions of fully or substantially hydrogenated block copolymers which have adequate viscosity and melt strength to ease processability, can be used in elastomeric applications and have a desirable balance of physical properties.
Additionally, uses for clear, substantially or fully hydrogenated block copolymers of vinyl aromatic and conjugated diene monomers, and polymer blends thereof, are still desired, wherein the copolymers are processable by conventional manufacturing technologies and possess useful physical properties at standard and elevated temperatures.